1. Field of the Invention
The present invention relates to a motor control device, an image forming apparatus, and a motor control method.
2. Description of the Related Art
In order to keep a rotation speed of a motor to a target speed, known has been a technique of measuring a period of a pulse signal that is output from an encoder in synchronization with rotation of the motor and performing feedback control such that the pulse period is closer to the target period corresponding to the target speed. There is the following concern for this technique. That is, when noise is superimposed on the pulse signal that is output from the encoder or when a phenomenon called chattering is generated, a measured pulse period is shorter than an actual period corresponding to the motor rotation speed, and stable control cannot be performed. In order to cope with this, proposed has been also a technique in which when the measured pulse period is shorter than a predetermined period, the measured pulse period is made invalid and feedback control is performed based on a previously measured pulse period (for example, see Japanese Patent No. 2886606).
In the technique as described in Japanese Patent No. 2886606, even when the previously measured pulse period is long and the currently measured pulse period is shorter than the predetermined period, feedback control is performed based on the previously measured pulse period. The control is performed in the above-mentioned manner even when the motor rotation speed is increased and the measured pulse period is shorter actually. Due to this, the motor rotation speed is controlled to be further increased, resulting in a problem that control stability is undermined.
Therefore, there is a need for a motor control device, an image forming apparatus, and a motor control method that are able of controlling a motor stably.